Measuring device for detecting the dimensions of test samples

ABSTRACT

A measuring device for detecting dimensions of bores has a light source emitting a light beam and a beamsplitter for splitting the light beam into a reference beam and a measuring beam. A reference mirror is arranged downstream of the beam splitter. The measuring beam is supplied to a measuring location of the bore and reflected on it. The reference beam is supplied to the reference mirror and reflected on it. The reflected beams are temporally incoherent and are recombined on the beamsplitter to form a recombined beam supplied to a receiver. Reference mirror and receiver have a lateral displacement relative to an optical axis of the measuring device, or the reference mirror is arranged laterally adjacent to the optical axis and the beam splitter at a slant to the optical axis. The measuring device is integrated into a tool or connected to a tool receptacle.

[0001] The invention relates to a measuring device for detectingdimensions of test samples according to the preamble of claim 1 or 5.

[0002] When manufacturing bores, seats, and the like in workpieces, itis necessary that the bores have a precise diameter. For this reason,the bores are measured with corresponding measuring devices after thedrilling process. When imprecise dimensions are detected, aftermachining is required.

[0003] The invention has the object to configure the measuring device ofthe aforementioned kind such that measuring is possible with greatprecision.

[0004] According to the present intention, this object is solved for ameasuring device of the aforementioned kind with the characterizingfeatures of claim 1 or 5.

[0005] With the measuring device according to the invention according toclaim 1 the dimensions of test samples, for example, the diameter ofbores in workpieces can be determined with high precision but still in asimple fashion. The beam which is emitted by the light source is dividedby the beamsplitter into a reference beam and into a measuring beam.While the measuring beam is deflected to the measuring location on thetest sample, the reference beam is deflected to a reference mirror.After reflection on the measuring location or the reference mirror, bothbeams are recombined and guided to the receiver. Because of thesuperposition of the beams, an interference contrast results based onwhich the desired information in regard to the measured dimension of thetest sample can be obtained.

[0006] Since the reference mirror and the receiver in regard to theoptical axis of the measuring device have a lateral displacement, thereference mirror and the receiver are thus not positioned on the opticalaxis but are positioned adjacent thereto. With such a configuration, avery high measuring precision can be obtained.

[0007] In the measuring device according to claim 5 the beamsplitter ispositioned at a slant to the optical axis of the measuring device. Inthis case, only the reference mirror is arranged adjacent to the opticalaxis of the measuring device while the light source and/or the receivercan be positioned on the optical axis.

[0008] Further features of the invention result from the additionalclaims, the description, and the drawing.

[0009] The invention will be explained in the following in more detailby means of an embodiment illustrated in the drawing. It is shown in:

[0010]FIG. 1 in a schematic illustration and in section a tool and adevice according to the present intention;

[0011]FIG. 2 an optical schematic of the measuring device according toFIG. 1;

[0012]FIG. 3 in a schematic illustration the function of the measuringdevice;

[0013]FIG. 4 a measuring signal which has been recorded with themeasuring device;

[0014]FIG. 5 an information flow schematic of the measuring deviceaccording to the invention arranged in a tool.

[0015] By means of the tool, dimensions on workpieces, preferably ofbores, can be measured simply and precisely. The measuring deviceprovided for this purpose is arranged in the tool which can be, forexample, a drilling tool or a thread milling cutter. With the measuringdevice it is also possible to measure groove depth or the bore depth ina workpiece. The measurement can be carried out during the machiningoperation performed by the tool. As a result of the measurement, thetool and/or the workpiece to be machined can be adjusted online untilthe nominal result is achieved. The machining result, for example,roundness of a bore or its diameter, is preferably directly measured andevaluated during machining. In this way, machining errors can bedetected and corrected immediately. The finishmachined workpiece doesnot require any additional check. Since a correction can be performedduring machining, very short machining times and primarily excellentproduct qualities can be obtained. Also, the tool service life isutilized optimally because, as a result of the online measurements andonline evaluation during machining, the tool can be used for machiningfor the optimal length of time.

[0016] It is also possible to perform with the tool machining onworkpiece and to measure and evaluate directly subsequently thereto themachining result. When the machining result does not conform to thedesired requirements, directly subsequently thereto the tool and/orworkpiece movement is corrected by the required amount and aftermachining is performed.

[0017]FIG. 1 shows a schematic illustration of a milling tool 1 with ashaft 34. By means of the tool a bore is drilled into a workpiece 2 asis known in the art. The tool 1 is embodied as a hollow body in which ameasuring device 4 is arranged. It has a housing 5 in which most of theelements of the measuring device 4 are arranged so as to be protected.It can be moved by means of a linear drive 6 in the axial direction ofthe tool 1. The tool 1 has near the free end at least one window 7through which in a way to be described in the following a measuring beamcan exit the tool 1 and reach the measuring location 8. In theillustrated embodiment, it is provided in the wall 9 of the bore 3.

[0018] The measuring device 4 has a light source 10 which is embodied asa broadband light source and advantageously is in the form of an LED.The light source 10, for example, can also be comprised of a halogenlamp, a superluminescent diode, a laser diode and the like. Downstreamthereof, a beamsplitter 11 is provided for deflecting the light emittedby the light source 10 to a lens system 15. It is comprised of acollimator 16, a lens 17, and an intermediately positioned beamsplitter18. On it a portion of the beam is reflected to a reference mirror 14.The lens system 15 is positioned on the axis of the measuring device 4.The reference mirror 14, the light source 10, and the beamsplitter 11are positioned outside of the optical axis of the measuring device 4.

[0019] The lens system 15 is illustrated in a simplified fashion. Thebeam path within the lens system 15 can deviate from the optical axis.

[0020] The lens system 15 has arranged downstream thereof a deflectionmirror 19 for deflecting the light beam 28 passing through thebeamsplitter 18 through the window 7 in the tool 1 to the measuringlocation 8 in the bore wall 9.

[0021] As illustrated in FIG. 1, the measuring device 4 has aninterferometer 31 which is arranged in the housing 5. The deflectionmirror 19 is outside of the housing 5 which is axially slidablysupported by means of a linear bearing 20 in the tool 1.

[0022] The light emitted by the light source 10 is deflected on thebeamsplitter 11 to the lens system 15. By means of the beamsplitter 18,a light beam 27 is reflected to the reference mirror 14 where this lightbeam is reflected back to the beamsplitter 18. The light beam 28 allowedto pass through the beamsplitter 18 is guided to the deflection mirror19 which guides the light beam onto the measuring location 8. The lightbeam is then reflected back to the deflection mirror 19. The light beam28 is then deflected from here to the beamsplitter 18.

[0023] By means of the beamsplitter 18, the light beam 27 reflected bythe reference mirror 14 and the light beam 28 coming from the deflectionmirror 19 are recombined and then guided to a receiver 13. It is anopto-electrical receiver, for example, in the form of a photo diode. Thereceiver 13 is positioned outside of the optical axis of the measuringdevice 4. Accordingly, the combined light beams 27, 28 are deflected onthe beamsplitter 11 to the receiver 13 as an interference beam.

[0024] The light beams 27, 28 received by the receiver 13 are nowsupplied to an analog-to-digital converter 21 whose converted digitalsignals are then evaluated by a computer 22 (FIG. 5) arrangeddownstream. The signal evaluation can be performed in an analog way.

[0025] The receiver 13 can also be an intelligent photosensor array withsignal broadening, for example, including A/D conversion and/or signalamplification. The obtained signals can be guided directly to thecomputer.

[0026] Since the bore wall 9 is to be measured about its periphery byinterference measurement, the measuring device 4 provided with theinterferometer 31 is rotated. It is possible to rotate the measuringdevice 4 within the tool 1 wherein, depending on the desired measuringprecision, the measuring device 4 is rotated about certain rotationalangles. Subsequently, the described interference measurement isperformed. As soon as the measuring result has been evaluated in thecomputer, the measuring device 4 is rotated by the next angular step. Inthis way, the entire periphery of the bore wall 9 can be measuresstep-wise. In this case, a corresponding number of windows 7 isprovided.

[0027] It is also possible to measure the entire tool 1 with themeasuring device 4 at a constant speed and to measure continuouslyduring the course of rotation.

[0028] The analog/digital converter 21 receives via an angle sensor 25and the clock generator 26 arranged downstream the required clocksignals. An angle sensor is not required when the angular position orthe rate of angular movement of the machine tool can be presetprecisely.

[0029] After a complete rotation of the tool 1 or of the measuringdevice 4, the measuring device, by means of the linear drive 6, or thetool 1, by means of the drive of the machine tool, is moved by thedesired amount so that the light beam exiting from the window 7 of thetool 1 impinges on a different peripheral plane of the bore wall 9. Thelinear movement of the measuring device 4 or of the interferometer 31 isrealized by a motor 6 (FIG. 5) arranged downstream of the computer 22(FIG. 5) and controlled by the computer by means of a motor drive 24.The linear movement of a sensor head 33 generated by the linear drive 6and guided in the linear bearing 20 is measured by a travel measuringsystem 35 and also controlled by it. The travel measuring system 35 isarranged within the tool 1. In the described way, the tool 1 and/or themeasuring device 4 is rotated about its axis in order to measure thebore wall 9 in the new axial position. In this way, the bore wall 9 canbe measured across a part of its axial length or even across its entireaxial length.

[0030]FIG. 5 shows schematically also the data transmission from therotating measuring system to the stationary computer 22. The data andenergy transmissions of the rotating measuring system 4 to thestationary computer 22 and the motor drive 24 is carried outbidirectionally and, as is known in the art, is realized by inductivecoupling 32 with sending and receiving parts as well as rotating andstationary antennas. FIG. 1 shows a further system location where thecoupling 32 can be provided, i.e., on the shaft of the tool.

[0031] Inasmuch as the measuring location 8 is located on the desireddiameter, the two beam paths of the reference and measuring arms 27, 28are of the same size. The measuring signal, which in FIG. 4 is shown inan exemplary fashion, has a maximum in this case. In the diagramaccording to FIG. 4 the intensity is plotted against the distance. Basedon the position of the maximum of the interference contrast, the radiusof the bore 9 can be determined. The intensity of the measuring signalresults in a way known in the art according to the following equation:

|(Δs)=I ₀{1+m y ₂₁ (Δs) cos (2π/λ·Δs+φ}

[0032] with the following meaning:

[0033] m=modulation factor

[0034] Y₂₁=bidirectional degree of coherence

[0035] λ=average wavelength

[0036] Δs=optical distance difference

[0037] φ=material-dependent phase jump.

[0038] The modulation factor m depends on the light intensity and thereflection factor. At the maximum of the interference signal (FIG. 4)the optical distance difference Δs is zero. By means of the measuringdevice 4 the optical distance difference Δs between the reference beam27 and the measuring beam 28 is tuned by moving the beamsplitter 18 inthe direction of the measuring beam 28, and the interference contrast(FIG. 4) detected in this way is evaluated. For example, when themeasuring location 8 deviates from the desired diameter, the measuringbeam 28 has a different length than the reference beam 27 which has aconstant length. The sensor head 33 is moved across the entire measuringarea and the interference signal is recorded in this way. Subsequently,the interference maximum is determined as a function of the traveleddistance. Based on this, the diameter of the bore can be determined.

[0039] Smaller shape deviations can be detected by moving the referencemirror 14 and recording the corresponding travel distance. In thisconnection, the interference signal is also recorded and theinterference maximum evaluated as a function of the travel distance.

[0040]FIG. 3 shows the principal function of the measuring device 4. Thelight emitted by the light source 10 is divided by the partiallytransmissive mirror 18 into the reflected beam 27 and into the passingbeam 28. The reflected beam 27 reaches in the described way thereference mirror 14 on which it is reflected back onto the splittermirror 18. The passing beam 28 impinges on the measuring location 8where it is reflected. The two partially coherent beams 27, 28 arerecombined on the splitter mirror 18 and cause interference. The twocombined beams then reach the receiver 13. The evaluation of theinterference contrast enables a resolution of less than 1 μm.

[0041] In the described measuring device 4 the light source 10, thereceiver 13, and the reference mirror 14 are not positioned on theoptical axis of the measuring device, but are separated by a lateraldisplacement. This arrangement reliably prevents particularlyreflections.

[0042] In a further embodiment (not illustrated), the beamsplitter 18 ispositioned slantedly. In this case, only the reference mirror 14 ispositioned adjacent to the optical axis. The light source 10 and thereceiver 13 in this case can be arranged on the optical axis of themeasuring device.

1. Measuring device for detecting dimensions of test samples, inparticular, of hollow bodies, preferably of recesses in workpieces,characterized in that the measuring device (4) can be integrated into atool (1) or, in place of a tool, can be connected to a tool receptacleand comprises at least one light source (10) whose light beams aredivided by a beamsplitter (18) into a reference beam (27) and ameasuring beam (28), of which the measuring beam (28) forming ameasuring arm can be supplied to a measuring location (8) of the testsample and the reference beam (27) forming a reference arm can besupplied to a reference mirror (14), wherein the temporally incoherentbeams reflected on the measuring location (8) and on the referencemirror (14) are recombined on the beamsplitter (18) and supplied to areceiver (13), and wherein the reference mirror (14) and the receiver(13) have a lateral displacement relative to the optical axis of themeasuring device (4).
 2. Measuring device according to claim 1,characterized in that the light source (10) and the reference mirror(14) have a lateral displacement relative to the optical axis of themeasuring device (4).
 3. Measuring device according to claim 1 or 2,characterized in that the beam splitter (18) guides the reference beam(27) directly onto the reference mirror (14).
 4. Measuring deviceaccording to one of the claims 1 to 3, characterized in that the axis ofthe reference beam (27) in the area between the beamsplitter (18) andthe reference mirror (14) extends angularly to the optical axis of themeasuring device (4).
 5. Measuring device for detecting dimensions oftest samples, in particular, of hollow bodies, preferably of recesses inworkpieces, characterized in that the measuring device (4) can beintegrated into a tool (1) or, in place of a tool, can be connected to atool receptacle and comprises at least one light source (10) whose lightbeams are divided by a beamsplitter (18) into a reference beam (27) anda measuring beam (28), of which the measuring beam (28) forming ameasuring arm can be supplied to a measuring location (8) of the testsample and the reference beam (27) forming a reference arm can besupplied to a reference mirror (14), which is positioned laterallyadjacent to the optical axis of the measuring device (4), wherein thetemporally incoherent beams reflected on the measuring location (8) andon the reference mirror (14) are recombined on the beamsplitter (18) andcan be supplied to a receiver (13), and wherein the beamsplitter (18) isarranged at a slant to the optical axis of the measuring device (4). 6.Measuring device according to claim 5, characterizing that the lightsource (10) is positioned on the optical axis of the measuring device(4).
 7. Measuring device according to claim 5 or 6, characterized inthat the receiver (13) is positioned on the optical axis of themeasuring device (4).
 8. Measuring device according to claim 1 to 7,characterized in that an optical travel difference (Δs) in the measuringarm or in the reference arm (27, 28) or in both arms can be tuned. 9.Measuring device according to one of the claims 1 to 8, characterized inthat the receiver (13) is connected to a computer (22) which evaluatesthe signals of the receiver (13).
 10. Measuring device according toclaim 9, wherein between the receiver (13) and the computer (22) ananalog/digital converter (21) is positioned.
 11. Measuring deviceaccording to one of the claims 1 to 10, characterized in that the tool(1) has at least one through opening (7) for the measuring beam (28)reaching the measuring location (8).
 12. Measuring device according toone of the claims 1 to 11, characterized in that the measuring device(4) is driven in rotation about its axis, preferably within the tool(1).
 13. Measuring device according to one of the claims 1 to 11,characterized in that the measuring device (4) can be rotated togetherwith the tool (1).
 14. Measuring device according to one of the claims 1to 13, characterized in that the measuring device (4) is arranged in ahousing (5) within the tool (1).
 15. Measuring device according to oneof the claims 1 to 14, characterized in that at least one part of themeasuring device (4) is movable in the direction of its axis. 16.Measuring device according to claim 15, characterized in that a lineardrive (6) is controlled by the computer (22).
 17. Measuring deviceaccording to claim 15 or 16, characterized in that the housing (5) ofthe measuring device (4) is axially movable within the tool (1). 18.Measuring device according to claim 15 or 16, characterized in that themeasuring device (4) together with the tool (1) is axially movable andthat for detecting the travel distance of the measuring device (4) atravel measuring system (35) is preferably provided which isadvantageously arranged in the tool (1).
 19. Measuring device accordingto one of the claims 1 to 18, characterized in that the reference mirror(14) is positioned outside of or on the axis of rotation of themeasuring device (4).